Typical, pistons used in a brake include one open end and one closed end. The open end faces the brake pad and the closed end is in contact with the brake fluid. When brake pressure is applied the fluid pressure increases and the fluid pushes on the closed end of the piston. The fluid moves the open end of the piston axially, with respect to a rotor, into contact with the brake pad so that the brake pad contacts the rotor and creates a braking force. The fluid pressure exerts both an axial force on the piston and a radial force on the piston. The axial forces on the piston move the piston into contact with the brake pad. Examples of such pistons are disclosed in U.S. Pat. Nos. 4,193,179; 6,637,317; and 7,000,526 all of which are expressly incorporated herein by reference for all purposes.
One disadvantage faced by these pistons is that the radial forces exerted on the closed end of the piston are relatively large. Due to the relatively large amount of radial force exerted on the closed end of the piston, the walls of the piston fail and the brake ceases to function properly. In order to avoid these failures, the walls of the piston are made relatively thick so that the piston does not fail. The added thickness of the piston walls increases the overall weight of the piston. However, the wall thickness of some pistons are not increased. These pistons are subject to an increased piston failure rate.
Another disadvantage faced by known pistons is that the choice of materials for use in creating the piston are limited. The material choice is limited to a material that is rigid so that it can withstand axial and radial forces, and it is important that the material does not degrade in brake fluid. Steel is a common choice used for making brake pistons. The steel is machined in order to create a piston, and due to the limitations in the machining process the possible configurations of the piston are limited. Alternatively, a piston may be molded out of a polymer, a thermoset, a glass fiber mold, or a reinforced thermo plastic and/or polymer. However, the wall thickness of pistons from such materials is typically thick so that the walls are rigid and can withstand both axial and radial forces. Thus, there is a need for a piston that is light, strong, resistant to failure, and does not increase the fluid displacement and/or the volume of the piston.